Cuprate-planes

This viewpoint is bolstered by the facts that both of the ruthenate materials GdSr2Cu2RuOg and Gd2.zCezSr2Cu2RuOio show magnetism (associated with their cuprate-planes) at low temperatures, which strongly indicates that their superconductivity is not in their cuprate-planes, but in their SrO layers [5],... 

The ruthenates and rutheno-cuprates are very similar to the cuprates in both sets of materials the Gd compound does not superconduct, either in Ba2GdRui-uCuu06 or in Gd2 zCezCuCV Also, once the superconductivity is located in the BaO or SrO planes (and not in the cuprate-planes) the... 

By placing the superconducting condensate in the SrO or BaO layers, and not in the cuprate-planes, we explain (i) why Ba2GdRuC>6 does not superconduct, (ii) why Gd2.zCezCuC>4 does not superconduct, and (iii) why Sr2YRu06 doped with Cu does superconduct - three facts that have been unexplained by cuprate-plane superconductivity. 

Figure 1. Cuprate-planar Cu charge extracted from the data, versus oxygen content x for YBa2Cu30x, as reported by Cava et al. (Ref. [1]) and by Jorgensen et al. (Ref. [2]). The two data sets do not follow the same line, because of calibration differences. The jump in the data of Ref. [1] occurs for only one datum, and is not reproduced in Ref. [2]. This calls into question claims that high-temperature superconductivity originates in the cuprate-planes.

There is a great deal of evidence that the cuprate-planes do not superconduct, not the least of which is that the cuprate-planes are sometimes adjacent to a magnetic (J O) pair-breaking rare-earth with L=0, such as Gd+3, which is unsplit by the crystal fields (because it has L=0). In such a case, as in the compound Gd2 Xe CuCk (which contains a CuC>2 plane, a Gd layer, an O2 layer, and a Gd layer) the Gd does break Cooper-like pairs and does destroy superconductivity in the adjacent layers (/Gd/O /Gd/). (An interstitial oxygen may also occupy a Gd layer.)... 

But Gd does not destroy superconductivity in GdBa2Cu307, despite being adjacent to a cuprate-plane, because the cuprate-plane does not superconduct and the superconductivity occupies the BaO layer. This pair of facts alone, that Gd2 sCe Cu() does not superconduct and GdBa2Cu3C>7 does,... 

This raises two questions (1) are the SrO layers (or the cuprate planes) of other superconducting materials the hosts of superconductivity and (2) do Sr2YRuOe s sister compounds, GdS C RuOs andGd2- Ce Sr2Cu2RuOio, superconduct in their cuprate planes or in their SrO layers ... 

Cuprate superconductors exhibit complicated phase diagrams which are functions of the doping parameter, x which controls the amount of the electron-transfer into or out of the cuprate plane. See for example Fig. 8.2. 

All the above numerical calculations were made in D=3 dimension. On the other hand it is widely known that, most of high Tc cuprates have layered structures with 2D CuO2 planes which play an essential role in the high Tc superconductivity.Therefore, it is nessesary to consider the dimensional contribution in the calculation.For this purpose,we consider the case of D = 2 + 2e (e / 0) in the post Gaussian approximation.In this case the optimal values of m and A also depend on e. Using Eq.(25) and the procedure outlined above one finds the e dependence of m2 presented in Fig.3 (solid line). 

Figure 8.5 Superconducting planes found in cuprate superconductors (a) a single Cu02 sheet and (b) a Cu02 (Q — Cu02) i superconducting layer.

The electron density in transition metal complexes is of unusual interest. The chemistry of transition metal compounds is of relevance for catalysis, for solid-state properties, and for a large number of key biological processes. The importance of transition-metal-based materials needs no further mention after the discovery of the high-Tc superconducting cuprates, the properties of which depend critically on the electronic structure in the CuOz planes. 

Plots of Tc vs in-plane rCu 0 for the series of p-type cuprate superconductors are grouped into three classes distinguished by the size of the 9-coordinate site cations (that is, La-, Sr- and Ba-classes) because of the combined electronic and nonelectronic effects. Every class of the Tc vs in-plane rCu 0 plot shows a maximum, so that every class of the p-type cuprate superconductors possesses an optimum hole density for which the Tc is maximum (40). 

Normally, additions depicted by model C lead to the highest asymmetric induction. The antiperiplanar effect of OR substituents can be very efficient in the Houk model B ( , , , , ) however it plays no role in model C. Furthermore, the Houk model B must be considered in all cycloaddition-like reactions. The Felkin-Anh model A is operative for nucleophilic additions other than cuprate additions ( ). The epoxidation reactions are unique as they demonstrate the activation of one diastereoface by a hydroxy group which forms a hydrogen bridge to the reagent ( Henbest phenomenon ). The stereochemical outcome may thus be interpreted in terms of the reactive conformations 1 and 2 where the hydroxy function is perpendicular to the olefinic plane and has an optimal activating effect. 

All the high Tc superconductors discovered so far, with one exception, contain weakly coupled copper oxide, Cu02, planes. The highest critical temperatures are found for cuprates containing a Group 2 metal (Ca, Ba, Sr) and a heavy metal such as Tl, Bi, or Hg. The structures of all the cuprate superconductors are based on, or related to, the perovskite structure. The one report (in 2000) of a non-cuprate high T superconductor is of surface superconductivity in Na WOs. The structure of NUxWOs is also based on the perovskite structure. 

The a/j-plane dc electrical resistivity of cuprate superconductors above is approximately linear in temperature over a wide range of several hundred degrees (Fig. 7.30). The slopes are nearly the same ( cs 1 cm/K) to within a factor of two for a wide range of single-crystal specimens. The extrapolated zero temperature intercept can be... 

Figure 7.30 The ab plane resistivity in cuprate superconductors as a function of temperature (a) Bismuth cuprate (2201) (b) Laj gjSro jjCuO (c) Bismuth cuprate (2212) (d) YBajCujO,.

Structural and electronic inhomogeneities are characteristic intrinsic properties of the cuprate superconductors related with the unconventional character of these compounds. The YBa2Cu30x (Y123x) compound is a prototype of cuprates with two Cu02 planes been extensively investigated over the 0oxygen concentration [1], The properties and the crystal structure of this material are closely related to x, with... 

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